Interfacial Interaction of Polymer/Liquid Crystal Molecules and Electrooptical Properties of their Composite Systems

Polymer/liquid crystal composite films were prepared from a solution of polymer and nematic liquid crystal (LC) by a solvent casting method. The phase-separated structure of the composite film was controlled by the solvent evaporation rate. The light-scattering profile of a poly(diisopropyl fumarate)/LC: 40/60 w/w solution during solvent evaporation exhibited a periodic structure, indicating that the phase-separated structure was formed by spinodal decomposition. The aggregation structure of the composite film was investigated with a scanning electron microscope (SEM). SEM observation of the composite film suggested the presence of periodicity and dual connectivity of polymer and LC phases. The faster the solvent was evaporated, the smaller the LC channel (domain) size in the composite film. The composite film, composed of poly(methyl methacrylate) (PMMA) and a nematic LC (E44) with a positive dielectric anisotropy, exhibited remarkable and reversible light-scattering-light-transmission switching, under the modulation of an ac electric field. The light-scattering state was dependent on such optical heterogeneities as spatial distribution of the nematic directors and/or mismatching in the refractive indices of the components. The electrooptical behavior of the composite film was strongly dependent on the LC channel (domain) size in the composite film. The transmittance increased and the rise and decay response times (τ_R and τ_D), decreased and increased, respectively, with an increase in the size of the LC channel (domain).

The electrooptical switching properties for the polymer/LC composite film should be influenced by miscibility between the polymer and the LC phases. The miscibility between both phases was evaluated from a distribution of relaxation time for interfacial polarization. The anchoring effect was also investigated by measuring the nonlinearity of the dielectric constant for the composite system.     

Three‐Step Spin State Transition and Hysteretic Proton Transfer in the Crystal of an Iron(II) Hydrazone Complex

A proton–electron coupling system, exhibiting unique bistability or multistability of the protonated state, is an attractive target for developing new switchable materials based on proton dynamics. Herein, we present an iron(II) hydrazone crystalline compound, which displays the stepwise transition and bistability of proton transfer at the crystal level. These phenomena are realized through the coupling with spin transition. Although the multi‐step transition with hysteresis has been observed in various systems, the corresponding behavior of proton transfer has not been reported in crystalline systems; thus, the described iron(II) complex is the first example. Furthermore, because proton transfer occurs only in one of the two ligands and π electrons redistribute in it, the dipole moment of the iron(II) complexes changes with the proton transfer, wherein the total dipole moment in the crystal was canceled out owing to the antiferroelectric‐like arrangement.     

Permselectivity of Gramicidin A Channels Based on Single‐channel Recordings

The expression mechanism of permselectivity through a gramicidin A (gA) channel between two aqueous phases (W1 and W2) was investigated. When the concentration of CsCl or CsBr in W1 was equivalent to that in W2, the single‐channel current was proportional to the absolute value of the applied membrane potential. Although the single‐channel current linearly increased with increasing electrolyte concentration in W1 and W2 until about 0.1 M (mol dm^?3), it began to level off around 0.1 M, indicating that ion permeation across the channel pore is the rate‐determining step and that the saturation of the transporting ion within the channel pore provokes the leveling off. In the case of asymmetric composition of the electrolyte in W1 and W2, the monovalent cation and the counter anion were transported in the opposite direction through the gA channel pore or the bilayer lipid membrane around the gA channel. Finally, the experimental data was fitted using the Goldman‐Hodgkin‐Katz equation based on the relationship between the membrane potential and the single‐channel current to define the ratio of the diffusion coefficients of Cs⁺, Cl^?, and Br^? as 5.7 : 1.0 : 0.26.     

A Convenient Synthesis of 2, 3 - DI- O - Acetyl-1, 6 - Anhydro- β - D – Glucopyranose

Abstract

1, 2, 3-Tri-O-acetyl-6-O-benzyl-4-O-chloroacetyl-α- and -β-D-glucopyranose (4α β)were derived from 1, 2, 3-tri-O-acetyl-4, 6- O -benzyl-idehe-β-D-giucopyranose (1) in two steps. Compound 1, 1, 2, 3-tri-O -acetyl-β-D-glucopyranose (2), and 4α,β were subjected to the cyclization reaction using Lewis acids ( SnCl₄ and BF₃-etherate), to give corresponding 1, 6-anhydro derivatives.     

Glycosylation Using Methylthioglycosides of N-Acetylneuraminic Acid and Dimethyl(Methylthio)Sulfonium Triflate

Abstract

Recently, great interest has been focussed on the synthesis of oligosaccharides containing N-acetylneuraminic acid (Neu5Ac) because of its important roles in a variety of biological recognitions.² However, many difficulties in the synthesis of naturally occurring α-glycosides still remained.³ We have recently reported the stereo-selective synthesis of a series of α- and β-2-thio-neuraminyl glycosides.^1-4

In the meantime, the utility of thioglycosides in oligosaccharide synthesis has been widely developed.⁵ Particularly noteworthy is the dimethyl(methylthio)sulfonium triflate (DMTST) promoted glyco-sylation method^5k.1 because excellent yields are achieved due to the high thiophilicity of this reagent.     

Cyclophane-lectin Conjugates as a New Class of Water-soluble Host

A conjugate composed of tetraaza[6.1.6.1]paracyclophane bearing carboxylic acids and lectin, a carbohydrate binding protein, was prepared. The specific saccharide-binding abilities as well as the secondary structural features of the lectin were not disturbed, when the cyclophane were covalently bound to the lectin. The conjugate was found to act as a water-soluble host for inclusion of anionic guest molecules such as 6-p-toluidino-naphthalene-2-sulfonate (TNS) and 8-anilinonaphthalene-1-sulfonate (ANS) in aqueous acetate buffer (pH 4.0) with binding constants of 4.2 × 10⁴ and 1.5 × 10⁴ dm³ mol⁻¹, respectively. The obtained binding constants were much larger than those by untethered water-soluble cyclophane. A highly desolvated microenvironment was provided by the cyclophane cavity on the protein surfaces so that the tight host–guest interaction, which brought about the marked motional repression of the entrapped guests, became effective. The conjugate also showed molecular discrimination capabilities toward the anionic guests through electrostatic repulsion mechanism originating from acid-dissociation equilibrium of carboxylic acids of the cyclophane branches.     

Investigation of proton diffusion in Nafion®117 membrane by electrical conductivity and NMR

The proton dynamics in Nafion ^®117 is investigated by comparison of the diffusion coefficient D_NMR estimated from PFG-NMR with that of D_σ estimated from electrical conductivity. At high water content region, D_σ is about two times higher than D_NMR as a result of Grotthuss mechanism. At low water content region, D_σ and D_NMR are in good agreement with each other. Both of the diffusion coefficients decrease steeply at low water content region. It can be explained as a result of the percolation transition due to the isolation of ion clusters, which is suggested by the recent small angle X-ray scattering data.     

Range Technique in Scattering Medium Using a Needle-Fiber Optical Coherence Tomography System

A needle-fiber optical coherence tomography (OCT) system designed for guiding epidural anesthesia to a target is presented. In the preliminary experiment, a desired target in tofu as a strong scattering medium can be monitored over a sufficient range of several millimeters within a short measuring time. The axial resolution is 21 μm. In order to investigate the ranging performance, the relation between background noise levels and focus-scattering properties in a confocal optical system is numerically studied by use of Monte Carlo technique. Numerical results indicate that an appropriate focal length of the lens attached to the fiber should be used to separate the OCT signal from strong noise in strongly scattered medium.     

Experimental and theoretical studies of Si-CN bonds to eliminate interface states at Si/SiO2 interface

Cyanide treatment, which includes the immersion of Si in KCN solutions followed by a rinse, effectively passivates interface states at Si/SiO₂ interfaces by the reaction of CN⁻ ions with interface states to form Si-CN bonds. X-ray photoelectron spectroscopy (XPS) measurements show that the concentration of the CN species in the surface region after the cyanide treatment is ∼0.25 at.%. Take-off angle-dependent measurements of the XPS spectra indicate that the concentration of the CN species increases with the depth from the Si/SiO₂ interface at least up to ∼2 nm when ultrathin SiO₂ layers are formed at 450 °C after the cyanide treatment. When the cyanide treatment is applied to metal-oxide-semiconductor (MOS) solar cells with 〈ITO/SiO₂/n-Si〉 structure, the photovoltage greatly increases, leading to a high conversion efficiency of 16.2% in spite of the simple cell structure with no pn-junction. Si-CN bonds are not ruptured by air mass 1.5 100 mW cm⁻² irradiation for 1000 h, and consequently the solar cells show no degradation. Neither are Si-CN bonds broken by heat treatment at 800 °C performed after the cyanide treatment. The thermal and irradiation stability of the cyanide treatment is attributable to strong Si-CN bonds, whose bond energy is calculated to be 1 eV higher than that of the Si-H bond energy using a density functional method.     

New class of cationic ring‐opening polymerizations of 2,2‐diphenyl‐1,3‐oxathiolanes accompanying quantitative elimination of benzophenone

Cationic polymerizations of three 2‐substituted 1,3‐oxathiolanes, 2,2‐diphenyl‐1,3‐oxathiolane ( 1a ), 5‐methyl‐2,2‐diphenyl‐1,3‐oxathiolane ( 1b ), and 4‐methyl‐2,2‐diphenyl‐1,3‐oxathiolane ( 1c ), were carried out with boron trifluoride etherate (BF₃ · OEt₂) in dichloromethane at 30 °C to obtain poly(alkylene sulfide)s accompanying the elimination of benzophenone. In the cationic polymerization of 1b and 1c , the consumption of the monomers and formation of benzophenone proceeded simultaneously. The obtained poly(propylene sulfide)s from 1b and 1c contain 41% head–head units, which is in good agreement with that of the polymer from methylthiirane with BF₃ · OEt₂. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2943–2949, 2004